The present invention relates to determination of optical properties, e.g. polarization dependent loss (PDL), polarization mode dispersion (PMD), differential group delay (DGD), insertion loss, return loss and/or chromatic dispersion (CD), of a device under test (DUT) in both directions in transmission and in reflection of an optical beam.
Measurement setups for the above-mentioned purpose shall be as easy as possible to handle and shall reveal all optical properties of the DUT as fast as possible and with as little handling as possible. This means that the DUT should be fully characterized to all parameters required when it is once connected to the measurement setup. For a full characterization it is required to measure all parameters both in transmission and in reflection as fast as possible.
From the disclosure of work of Sandel et al (David Sandel, Reinhold Noé, “Optical Network Analyzer applied for Fiber Bragg Grating Characterization”, ECOC 97, 22-25 Sep. 1997, Conference Publication No. 448, © IEE, 1997, pp. 186-189; David Sandel et al, “Optical Network Analysis and Longitudinal Structure Characterization of Fiber Bragg Grating”, Journal of Lightwave Technology, Vol. 16, No. 12, December 1998, pp. 2435-2442) it is known a method for polarization-resolved optical fiber Bragg grating characterization. However, in these disclosures only the reflection of the DUT is measured.
From a work of Froggatt at al (Froggatt et al, “Full Complex Transmission and Reflection Characterization of a Bragg Grating in a Single Laser Sweep”, ) it is known a measurement setup to measure the group delay of a DUT in transmission and in reflection in both directions.
However, with the disclosed measurement setup it is not possible to measure PMD or PDL. Moreover, the measurement setup disclosed in this article causes problems because to enable the detectors used to detect the signals of reflection and transmission of both directions simultaneously, i.e. the reflected signal of one direction superimposed with the transmitted signal of the other direction and the transmitted signal of one direction superimposed with the reflected signal of the other direction, differences between the measurement and the reference path lengths are necessary to distinguish between these signals without really knowing all impacts of these differences.
Also the different path lengths for the various signals put additional requirements onto the receiver characteristics and the DUT characteristics which may be problematic for an accurate measurement.